1. Field of the Invention
This invention relates to a plate lens comprising a transparent base which has flat surfaces and which serves as a lens, and to a method for manufacturing the same. The plate lens of this type may be used in various types of display devices using LEDs, faceplates of CRTs, or the like.
2. Description of the Prior Art
A CRT generally comprises a thick glass plate so as to withstand a relatively high vacuum. Light emitted from a phosphor which is coated on the inner surface of a glass plate of a faceplate of the CRT is dispersed during transmission through the faceplate. This causes interference between light emitted from adjacent portions of the phosphor and degrades the clarity of the overall image.
In view of this problem, a CRT is known which uses as a faceplate a fiber plate which is obtained by bundling a number of optical fibers parallel to each other and fusing the fibers together into a flat plate. A CRT of this type is mainly used for data transmission/reception in a facsimile system. However, with the faceplate of the type described above, the amount of light transmitted through the individual optical fiber is relatively small in relation to that of light which becomes incident on the total area of the plate, so that a satisfactory brightness may not be obtained. If small air bubbles or other foreign materials are trapped in the interface between the fused optical fibers, they impair the resistance to a high vacuum and withstand voltage characteristics of the resultant faceplate, thus rendering manufacture of the faceplate difficult. For this reason, if a faceplate of this type is to be used as a faceplate of a CRT having a relatively large area such as a TV, the faceplate becomes extremely expensive to manufacture and is not therefore practical.
Meanwhile, in a general display device which has a number of light sources such as LEDs and which selectively turn on/off to display an image, improvements in contrast of the image are desired.